Class PushbackInputStream
java.lang.Object
java.io.InputStream
java.io.FilterInputStream
java.io.PushbackInputStream
- All Implemented Interfaces:
Closeable,AutoCloseable
A
PushbackInputStream adds
functionality to another input stream, namely
the ability to "push back" or "unread" bytes,
by storing pushed-back bytes in an internal buffer.
This is useful in situations where
it is convenient for a fragment of code
to read an indefinite number of data bytes
that are delimited by a particular byte
value; after reading the terminating byte,
the code fragment can "unread" it, so that
the next read operation on the input stream
will reread the byte that was pushed back.
For example, bytes representing the characters
constituting an identifier might be terminated
by a byte representing an operator character;
a method whose job is to read just an identifier
can read until it sees the operator and
then push the operator back to be re-read.- Since:
- 1.0
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected byte[]The pushback buffer.protected intThe position within the pushback buffer from which the next byte will be read.Fields declared in class java.io.FilterInputStream
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Constructor Summary
ConstructorsConstructorDescriptionCreates aPushbackInputStreamwith a 1-byte pushback buffer, and saves its argument, the input streamin, for later use.PushbackInputStream(InputStream in, int size) Creates aPushbackInputStreamwith a pushback buffer of the specifiedsize, and saves its argument, the input streamin, for later use. -
Method Summary
Modifier and TypeMethodDescriptionintReturns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream.voidclose()Closes this input stream and releases any system resources associated with the stream.voidmark(int readlimit) Marks the current position in this input stream.booleanTests if this input stream supports themarkandresetmethods, which it does not.intread()Reads the next byte of data from this input stream.intread(byte[] b, int off, int len) Reads up tolenbytes of data from this input stream into an array of bytes.voidreset()Repositions this stream to the position at the time themarkmethod was last called on this input stream.longskip(long n) Skips over and discardsnbytes of data from this input stream.voidunread(byte[] b) Pushes back an array of bytes by copying it to the front of the pushback buffer.voidunread(byte[] b, int off, int len) Pushes back a portion of an array of bytes by copying it to the front of the pushback buffer.voidunread(int b) Pushes back a byte by copying it to the front of the pushback buffer.Methods declared in class java.io.FilterInputStream
readMethods declared in class java.io.InputStream
nullInputStream, readAllBytes, readNBytes, readNBytes, skipNBytes, transferTo
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Field Details
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buf
protected byte[] bufThe pushback buffer.- Since:
- 1.1
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pos
protected int posThe position within the pushback buffer from which the next byte will be read. When the buffer is empty,posis equal tobuf.length; when the buffer is full,posis equal to zero.- Since:
- 1.1
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Constructor Details
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PushbackInputStream
Creates aPushbackInputStreamwith a pushback buffer of the specifiedsize, and saves its argument, the input streamin, for later use. Initially, the pushback buffer is empty.- Parameters:
in- the input stream from which bytes will be read.size- the size of the pushback buffer.- Throws:
IllegalArgumentException- ifsize <= 0- Since:
- 1.1
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PushbackInputStream
Creates aPushbackInputStreamwith a 1-byte pushback buffer, and saves its argument, the input streamin, for later use. Initially, the pushback buffer is empty.- Parameters:
in- the input stream from which bytes will be read.
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Method Details
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read
Reads the next byte of data from this input stream. The value byte is returned as anintin the range0to255. If no byte is available because the end of the stream has been reached, the value-1is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.This method returns the most recently pushed-back byte, if there is one, and otherwise calls the
readmethod of its underlying input stream and returns whatever value that method returns.- Overrides:
readin classFilterInputStream- Returns:
- the next byte of data, or
-1if the end of the stream has been reached. - Throws:
IOException- if this input stream has been closed by invoking itsclose()method, or an I/O error occurs.- See Also:
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read
Reads up tolenbytes of data from this input stream into an array of bytes. This method first reads any pushed-back bytes; after that, if fewer thanlenbytes have been read then it reads from the underlying input stream. Iflenis not zero, the method blocks until at least 1 byte of input is available; otherwise, no bytes are read and0is returned.- Overrides:
readin classFilterInputStream- Parameters:
b- the buffer into which the data is read.off- the start offset in the destination arrayblen- the maximum number of bytes read.- Returns:
- the total number of bytes read into the buffer, or
-1if there is no more data because the end of the stream has been reached. - Throws:
NullPointerException- Ifbisnull.IndexOutOfBoundsException- Ifoffis negative,lenis negative, orlenis greater thanb.length - offIOException- if this input stream has been closed by invoking itsclose()method, or an I/O error occurs.- See Also:
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unread
Pushes back a byte by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value(byte)b.- Parameters:
b- theintvalue whose low-order byte is to be pushed back.- Throws:
IOException- If there is not enough room in the pushback buffer for the byte, or this input stream has been closed by invoking itsclose()method.
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unread
Pushes back a portion of an array of bytes by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the valueb[off], the byte after that will have the valueb[off+1], and so forth.- Parameters:
b- the byte array to push back.off- the start offset of the data.len- the number of bytes to push back.- Throws:
NullPointerException- Ifbisnull.IOException- If there is not enough room in the pushback buffer for the specified number of bytes, or this input stream has been closed by invoking itsclose()method.- Since:
- 1.1
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unread
Pushes back an array of bytes by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the valueb[0], the byte after that will have the valueb[1], and so forth.- Parameters:
b- the byte array to push back- Throws:
NullPointerException- Ifbisnull.IOException- If there is not enough room in the pushback buffer for the specified number of bytes, or this input stream has been closed by invoking itsclose()method.- Since:
- 1.1
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available
Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes.The method returns the sum of the number of bytes that have been pushed back and the value returned by
available.- Overrides:
availablein classFilterInputStream- Returns:
- the number of bytes that can be read (or skipped over) from the input stream without blocking.
- Throws:
IOException- if this input stream has been closed by invoking itsclose()method, or an I/O error occurs.- See Also:
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skip
Skips over and discardsnbytes of data from this input stream. Theskipmethod may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly zero. Ifnis negative, no bytes are skipped.The
skipmethod ofPushbackInputStreamfirst skips over the bytes in the pushback buffer, if any. It then calls theskipmethod of the underlying input stream if more bytes need to be skipped. The actual number of bytes skipped is returned.- Overrides:
skipin classFilterInputStream- Parameters:
n- the number of bytes to be skipped.- Returns:
- the actual number of bytes skipped.
- Throws:
IOException- if the stream has been closed by invoking itsclose()method,in.skip(n)throws an IOException, or an I/O error occurs.- Since:
- 1.2
- See Also:
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markSupported
public boolean markSupported()Tests if this input stream supports themarkandresetmethods, which it does not.- Overrides:
markSupportedin classFilterInputStream- Returns:
false, since this class does not support themarkandresetmethods.- See Also:
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mark
public void mark(int readlimit) Marks the current position in this input stream.The
markmethod ofPushbackInputStreamdoes nothing.- Overrides:
markin classFilterInputStream- Parameters:
readlimit- the maximum limit of bytes that can be read before the mark position becomes invalid.- See Also:
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reset
Repositions this stream to the position at the time themarkmethod was last called on this input stream.The method
resetfor classPushbackInputStreamdoes nothing except throw anIOException.- Overrides:
resetin classFilterInputStream- Throws:
IOException- if this method is invoked.- See Also:
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close
Closes this input stream and releases any system resources associated with the stream. Once the stream has been closed, further read(), unread(), available(), reset(), or skip() invocations will throw an IOException. Closing a previously closed stream has no effect.- Specified by:
closein interfaceAutoCloseable- Specified by:
closein interfaceCloseable- Overrides:
closein classFilterInputStream- Throws:
IOException- if an I/O error occurs.- See Also:
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